Lamina implant and method

ABSTRACT

A prosthetic implant for restoring lamina after a laminectomy. The implant is generally a lamina-sized construct having a hollow interior. The lamina removed during the laminectomy may be converted to autologous bone that may then be placed inside the hollow interior of the implant. The implant may then be secured to the spine at the site of the laminectomy so that lamina restoration can occur as the hollow interior of the implant solidifies with bone growth.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 15/236,528, dated Aug. 15, 2016, which is a continuation ofU.S. patent application Ser. No. 14/803,154, dated Jul. 20, 2015, whichis a continuation of U.S. patent application Ser. No. 13/940,217, filedJul. 11, 2013, now U.S. Pat. No. 9,138,325, which claims the benefit ofU.S. Provisional Patent Application Ser. No. 61/670,581 filed Jul. 11,2012, and these applications are incorporated herein by reference intheir entireties for all purposes.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates to the field of lamina replacement.

2. Description of the Related Art

Laminectomies, removal of the spinal lamina, are the most commonsurgical procedures in spinal surgery. Laminectomies are routinelyperformed in the cervical and lumbar spine to allow decompression of keyareas of the spine.

Cervical laminectomies allow decompression of the spinal cord and nerveroots. Patients may present with a radiculopathy (pain in the arms),myelopathy (weakness in arms and legs), or a combination of both.Cervical laminectomies are performed over multiple cervical levels andare an effective technique for cervical decompression and relief ofsymptoms. Removal of the posterior spinal elements, the cervical lamina,predisposes the patient to develop spinal instability, deformity, andpain. The posterior spinal elements, lamina, allow posterior structuralsupport for the spine and an attachment for the posterior neck muscles.Some surgeons will perform a spinal fusion after cervical laminectomy toprevent spinal deformity. Cervical fusion creates an unnatural state forthe neck, however, as the entire fused neck segment is non-mobile. Thereis a high risk of adjacent level segment instability after cervicalfusion since all of the force with motion is transferred to the segmentabove and below the fusion.

Cervical laminoplasty has been devised for decompression andreconstruction of the cervical lamina, but has certain limitations thathave decreased its usefulness in spinal surgery. The primary issue isthe technical difficulty of cervical laminoplasty. A “trough” needs tobe drilled on one side of the junction of the lamina and lateral mass.This is a technically challenging technique. After a complete trough isformed on one side of the lamina-lateral mass junction, a partial troughis then formed on the opposite side. The lamina is then lifted off thedura and a wedge of bone is secured between the lifted-up side of thelamina Therefore, current cervical laminoplasty techniques allowadequate decompression of only one side of the spinal cord and nerveroots.

Lumbar laminectomies are performed for decompression of the cauda equinaand nerve roots. As a large laminectomy defect is created, however,spinal instability can occur. There can also be additional scarformation, as the muscle has to rest directly on the dura after atraditional laminectomy. Some surgeons use hemilaminotomies, where onlya portion of the lamina is removed to decompress the nerve roots.However, hemilaminotomies are technically difficult, time consuming, andcannot adequately decompress the bilateral nerve roots and central dura.Lumbar fusions are routinely performed after lumbar laminectomies, butrepresent a plethora of technical difficulties and predispose thepatient to “adjacent level” instability as forces are displaced above orbelow the fusion. A fusion also involves the placement of large pediclescrews through the pedicle of the vertebral body. Misplacement of thescrews has resulted in cerebrospinal fluid (CSF) leaks, nerve injury,and paralysis.

As such, there is still a need for a prosthetic implant for restoringthe lamina after laminectomies while providing complete relief for thepatient.

SUMMARY OF THE INVENTION

The present invention is directed towards a prosthetic implant forrestoring lamina after a laminectomy. The implant is generally alamina-sized construct having a hollow interior. The lamina removedduring the laminectomy may be converted to autologous bone that may thenbe placed inside the hollow interior of the implant. The implant is thensecured to the remaining portion of the spine at the site of thelaminectomy. An attaching agent, such as one or more plates with screws,may be used to secure the implant to the spine. Over time, theautologous bone inside the hollow interior of the implant will solidifyas bone grows through the interior of the implant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of the spine with the lamina removed.

FIG. 2A shows a rear view of the cervical region of the spine with thelamina removed with an embodiment of the present invention in place.

FIG. 2B shows a rear view of the lumbar region of the spine with thelamina removed with an embodiment of the present invention in place.

FIG. 3 shows a perspective view of an embodiment of the presentinvention with its parts separated and the attachment sites of thespine.

FIG. 4 show a cross-sectional perspective view of an embodiment of thepresent invention secured to the spine.

FIG. 5 shows a cross-sectional isometric top view of an embodiment ofthe present invention secured to the spine after bone growth.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of presently-preferred embodimentsof the invention and is not intended to represent the only forms inwhich the present invention may be constructed and/or utilized. Thedescription sets forth the functions and the sequence of steps forconstructing and operating the invention in connection with theillustrated embodiments. It is to be understood, however, that the sameor equivalent functions, features, and sequences may be accomplished bydifferent embodiments that are also intended to be encompassed withinthe spirit and scope of the invention.

The present invention represents a novel implant and technique for therestoration of the lamina after cervical decompression or lumbardecompression. As seen in FIG. 1, when a surgeon performs a cervical orlumbar laminectomy by removing the lamina 102 of a spine 100, a gap isformed. In one embodiment of the present invention, an appropriatelysized lamina replacement implant 200 may then be selected for attachmentto the spine 100 on each side 106 of the gap.

This embodiment of the present invention, therefore, includes a laminareplacement implant 200. As shown in FIG. 2A and FIG. 2B, it may besecured to the spine 100 at the site of the removed lamina The implant200 is shaped in a way that allows attachment to the spine 100 whileproviding support for the spine 100 and/or protection for the spinalcord 108. In a preferred embodiment, the implant 200 has a hollow bodyhaving a first arm 202 terminating at a first end 204, a second arm 206terminating at a second end 208, connected together in a mid-section210. The hollow body may be made of PEEK (polyether ether ketone) orother suitable biocompatible material.

In the embodiment in FIG. 3, the body of the implant 200 has a first arm202 and a second arm 206, with the first arm 202 and the second arm 206connected to form the mid-section 210. In this embodiment, the first arm202 and second arm 206 are connected in a movable way to allow foradjustments to their orientation. Examples include the use of hinges,pivots, joints, or telescoping features. This allows the implant 200 tobe adjusted to fit many of the different sizes of the spine 100 atdifferent spinal levels. Accordingly, one such implant 200 could beadjusted outwardly to fit the largest lumbar spinal level or inwardly tofit a much smaller cervical spinal level so that it may be applicable tomany or all of the spinal levels. Alternatively, a larger two-armimplant 200 could be fashioned to fit just the lumbar spinal levels anda smaller two-arm implant could be fashioned to fit just all or aportion of the cervical spinal levels. Once the adjustment has been madesuch that the ends of the two arms satisfactorily mate with the spine100, this particular orientation can be locked in place by a lockingmechanism 218, such as a screw, pin, glue, or any equivalents. Thelocking mechanism may be made of titanium, solidified bone graftmaterial, or other biocompatible material. The two arms would mate withthe lateral mass in the cervical spine and facet/pedicle in the lumbarspine.

In another embodiment, the body of the implant 200 is one piece or evenmultiple pieces but without a defined hinge or pivot portion. Such animplant 200 could have several mounting holes or slots so as to be ableto mount to a range of spinal levels of several different sizes.Alternatively, such an embodiment could involve two flexible arms 202,206 or a flexible mid-section 210. The flexible portion could be elasticsuch that it tends to spring back to a neutral shape until it is fixedto the spine 100. Yet a further alternative would be that the flexibleportion could be designed to readily plastically deform so that there isno significant tendency of the implant 200 to return to a neutral shapeonce flexed.

Once the surgeon adjusts the implant 200 and moves it into place, suchas in FIGS. 2, 4 and 5, the surgeon may secure the implant 200 to thespine 100. This can be done by several different securing means. In theembodiment shown in FIG. 4, the implant 200 is secured to the spine 100using plates, braces, or brackets fixed to the implant 200 and/or thespine 100 by screws 214, 216 Implant screws 214 of appropriate lengthmay attach the plates 212 to the arms 202, 206 of the implant 200, andspinal screws 216 of appropriate length may attach the plate 212 to thespine 100. In one preferred embodiment, the lengths are approximately 6mm-8 mm for the cervical region and approximately 12 mm-14 mm for thelumbar region. In another embodiment, the plates 212 and screws 214, 216may comprise titanium or a titanium alloy for their biocompatibleproperties. In other embodiments, the securing means may instead be amalleable strap, a biodegradable material, or a durable or biodegradableadhesive.

The implant 200 should be attached so as to allow contact between theremaining portions of the exposed spine 100 and a region on or in theimplant 200 that comprises a bone graft region 300 that can facilitatebone growth through the implant 200. In one embodiment, at least aportion of the implant 200 may be hollow. These hollow portions 300 canbe fitted securely so any bone graft material 500 will not leak out. Ina preferred embodiment, the first and second ends of the arms alsocomprise bevels to allow the implant to more securely attach to thespine. When that midsection is adjusted, the angle of the bevels maychange orientation as well. Because of this, in some embodiments, themating faces of the arms may also be adjustable, malleable, orrealignable so that the bevels are at a correct orientation to securelyattach to the lateral mass 106 for ease of mating and alignment with thespine and to better ensure a tight fit therebetween. To furtherfacilitate securement to the spine 100, the first and second ends mayfurther comprise one or more notches into which remaining portions ofthe spine are contoured, fitted or wedged. One or more additionalbuffers, such as linings, gap-filling adhesives, mating gaskets, orcushioning, may be added to prevent any leakages of bone graft material500 from the secured implant 200 or to better fit and secure the implantto the spine 100. The spine and/or the ends of the arms may be furthershaped to each other's contours to form a more secure attachment. Theinclusion of adjustable mating facings further reduces the time andeffort required in contouring, fitting, or wedging the implant or spine.

Thus, in one embodiment, a hollow interior 300 of the implant 200 may befilled with bone graft material 500 that is intended to solidify throughthe implant. As shown in FIG. 5, the bone graft material 500 may becomeas strong as bone and provide additional strength for the implant 200.In one embodiment, after a spinal laminectomy, the removed portions oflamina may be crushed into autologous bone (autograft) and used as bonegraft material 500 in the implant 200. This would aid the implant 200 tosolidify over time as bone continues to grow through the implant 200.Such autologous bone graft material 500 may also decrease the chancesthat such material will be rejected by the patient's body. Indeed, PEEKimplants in spinal surgery, filled with autograft and fitted in the discspace, have shown to produce robust bone growth through the interiorwhere autograft has been placed. As PEEK has modules of elasticity thatresemble that of bone, it may be a preferential template for laminareplacement, although other compositions may be used and newcompositions are sure to prove useful with advancements in the field.

Alternatively, the bone graft material 500 could be composed ofautograft material from other portions of the body, allograft materialfrom the bones of other people (such as cadavers, donors, or stem cellcultures), xenograft material from animals, synthetic replacements,other similar substitutes, or a combination thereof. In one embodiment,the implant uses larger bone pieces or fragments or other bone graftmaterial that may have been pre-solidified or partially solidifiedbefore it is implanted into a patient.

In one embodiment, as shown in FIG. 5, the surgeon may drill into theexposed sections of the spine 100 and fill the void created thereby withbone graft material 500 that is also used to fill adjacent hollowportions 300 of the implant 200 so that new bone formed inside the endsof the implant and the new bone formed inside the drilled void withinthe adjacent spine can form together, allowing for a more secure boneattachment. The embodiment in FIG. 5 shows a drilled area with roundededges, but other shapes may be used for stronger securement or greatersurface areas. In one embodiment, a drill with a hollow center is usedso the drilled area has a peg in the middle for greater surface area topromote bone growth. In another embodiment, several holes are drilled ineach lateral mass 106 for increased surface area. Alternatively, theimplant 200 may include a solid end mass that approximately mates withthe interior surface of the void created in the spine 100 and designwith a surface material and/or texture that facilitates bone growth orsolidification, such surfaces may include nanostructured regions,including nanotextured and nanoporous regions. The solid end mass mayalso be a solid nub used for anchoring the implant in the bone. Thissolid nub can be made from titanium, bone made from bone graft material,or other biocompatible material.

Additionally, the implant portions themselves may be composed ofbiodegradable materials so that the bone graft material 500 solidifieswith the spine 100 and the biodegradable implant later biodegradesultimately to restore the spinal lamina 102.

While the present invention has been described with regards toparticular embodiments and some of their equivalents, it is recognizedthat additional variations of the present invention with theirfunctionally equivalent features may be devised without departing fromthe inventive concept.

What is claimed is:
 1. An implant for lamina replacement and restorationof a spine, the implant comprising: a first arm, a second arm, a hingeconnected therebetween such that the first arm and the second arm aremovably connected to each other through the hinge, and a hollow interiorthat extends from the hinge to a distal end of the first arm and adistal end of the second arm; and a first securing member configured tosecure the first arm to a first portion of the spine and a secondsecuring member configured to secure the second arm to a second portionof the spine, wherein each of the first and second arms includes a solidend mass configured to mate with a portion of a spine and having atleast one of a surface material and texture configured to facilitatebone growth.
 2. The implant of claim 1, wherein the at least one of asurface material and texture include nanostructured regions.
 3. Theimplant of claim 1, wherein the first and second securing membersinclude plates, braces, or brackets and one or more spinal screws. 4.The implant of claim 1, wherein the hinge is configured to lock a givenorientation of the first arm relative to the second arm.
 5. The implantof claim 1, wherein the hollow interior is filled with bone graftmaterial.
 6. The implant of claim 5, wherein the bone graft material isautologous bone.
 7. The implant of claim 5, wherein the bone graftmaterial is allograft bone, xenograft bone, or synthetic material. 8.The implant of claim 1, wherein the implant is adjustable in shape orsize to fit different spinal levels.
 9. The implant of claim 1, whereinthe first and second arms are flexible.
 10. An implant for laminareplacement and restoration of a spine, the implant comprising: a firstarm and a second arm, wherein the first arm and second arm connect toform a mid-section, and the mid-section allows the first arm and secondarm to be movable relative to one another, and a hollow interior thatextends from the mid-section to a distal end of the first arm and adistal end of the second arm; and a first securing member configured tosecure the first arm to a first portion of the spine and a secondsecuring member configured to secure the second arm to a second portionof the spine, wherein each of the first and second arms includes a solidend mass configured to mate with a portion of a spine and having atleast one of a surface material and texture configured to facilitatebone growth.
 11. The implant of claim 10, wherein the mid-sectioncomprises a hinge, a pivot, a joint, or a telescoping feature.
 12. Theimplant of claim 10, wherein the mid-section comprises a hinge.
 13. Theimplant of claim 10, further comprising a locking mechanism configuredto lock the first arm with respect to the second arm.
 14. The implant ofclaim 10, wherein the first and second arms are flexible.
 15. Theimplant of claim 10, wherein the at least one of a surface material andtexture include nanostructured regions.
 16. The implant of claim 10,wherein the first and second securing members include plates, braces, orbrackets and one or more spinal screws.
 17. The implant of claim 10,wherein the hollow interior is filled with bone graft material.
 18. Theimplant of claim 17, wherein the bone graft material is autologous bone.19. The implant of claim 17, wherein the bone graft material isallograft bone, xenograft bone, or synthetic material.
 20. The implantof claim 10, wherein the implant is adjustable in shape or size to fitdifferent spinal levels.